JP5922564B2 - Distributed radio communication base station system and communication method - Google Patents

Description

  The present invention relates to a communication method between base stations in a distributed radio communication base station system including a plurality of radio communication base stations and a PON (Passive Optical Network) transmission system.

  An area in which a base station provides services to a mobile station in a mobile communication system is called a cell. When the base station outputs radio signal radio waves with an omnidirectional antenna, the cell spreads concentrically around the base station, and the radius changes according to the transmission output level of the antenna. In order to efficiently use radio frequency bands, base stations are installed with high geographical density, cells that are the reach of radio waves are kept in a certain area, and the same frequency band is reused as much as possible spatially. It has been broken.

  FIG. 1 shows an example of a communication environment in a cellular system. When the mobile station moves in the cell and reaches the end region of the cell, the strength of the signal (solid line) from the communicating base station 103A is weakened, while the signal received from the adjacent base station 103B (broken line) ) Is relatively strong. As a result, as shown in FIG. 1, in the area where the cell 102A and the cell 102B overlap, the downlink communication is more affected by the interference signals of the adjacent base stations 103A and 103B. Signal reception sensitivity decreases.

  Further, when the mobile station 101 moves and enters the area of the cell 102B of the adjacent base station 103B, the communication is continued by switching the belonging base station from 103A to 103B. This series of procedures is generally called handover. As the mobile station 101 moves between cells from 102A to 102B, there arises a problem that the transmission rate is remarkably lowered in the state before and after the handover, that is, in the state where the mobile station 101 is located at the cell edge. For this reason, there is a problem in realizing communication quality that is stable in terms of area.

  In order to solve the problem of communication quality degradation caused by signal interference between adjacent base stations, various measures have been studied so far. One of the measures is a method of suppressing a decrease in communication quality by allowing base stations adjacent to a mobile station located at the cell edge to communicate with each other in cooperation with each other. This method is generally called coordinated multi-point transmission / reception (CoMP) between base stations (cells) (Non-Patent Document 1).

  There are several implementation methods for CoMP, but there is a Joint Transmission (JT) system as one of implementation methods for CoMP for a downlink signal. The JT method is a method for improving the gain of a received signal of a terminal by transmitting the same downlink signal from an adjacent base station to a mobile station located at a cell edge. JT is studying two methods: non-coherent transmission that uses soft combining (combining) reception of radio signals and coherent transmission that realizes in-phase combining of signals at reception points by performing precoding across cells. . Both cases are common in that the mobile station improves the gain by simultaneously receiving the same signal from two or more base stations, and as a result, the communication quality of the mobile station located at the cell edge is improved. An effect is obtained.

  In non-coherent transmission that is easier to implement among these two JT implementation methods, adjacent base stations transmit the same radio signal to a mobile station. However, a mobile core network (Evolved Packet Core: EPC) sends RAN ( It is necessary to transmit the same downlink signal to each base station via Radio Access Network). As the method, for example, in the LTE (Long Term Evolution) system standardized in 3GPP (Third Generation Partnership Project), there are roughly two procedures as shown in FIG. 2 (a) and FIG. 2 (b). That is, a method of transmitting a user plane signal from each EPC to each base station via the S1 interface (FIG. 2 (a)), and a signal received by the base station requesting JT once buffered. 2 is a method of copying the signal used in (1) and transmitting it to other base stations participating in JT via the X2 interface (FIG. 2B).

FIG. 3 shows an example of a flowchart when JT is performed via the related X2 interface. The operation procedure is described below.
Step S301: Data addressed to the mobile station X is transmitted from the MME / S-GW to the base station A.
Step S302: The base station A acquires information on neighboring cells based on information from the mobile station X. Specifically, information such as the signal reception level of the downlink signal from the adjacent cell and the signal-to-noise interference power ratio (SINR) reported from the mobile station X is used.
Step S303: When the reception level of the signal from the adjacent cell reaches a preset threshold value, the base station A determines that the mobile station X exists at the end of the cell with the adjacent cell. At the same time, the base station B subject to JT is specified. Base station A then issues a JT cooperation request to base station B. At this time, control information such as radio band allocation information related to the mobile station is also notified.
Step S304: The base station B determines whether or not cooperation with the base station A is possible. The case where the base station B determines that the cooperation is impossible occurs, for example, when a resource shortage occurs, for example, the radio band of the mobile station X transmitted from the base station A is not free due to the radio band allocation of the base station B. sell. In other cases, the base station B replies that cooperation is possible (cooperation response).
Step S305: The base station B returns to the base station A whether cooperation is possible. The case where the base station B replies that cooperation is impossible occurs when, for example, a shortage of resources occurs, for example, the radio band of the mobile station X transmitted from the base station A is not free due to the radio band allocation of the base station B. sell. In other cases, the base station B replies that cooperation is possible (cooperation response).
Step S <b> 306: The base station A that has received the cooperable signal (cooperation response) transfers the data addressed to the mobile station X to the base station B.
Step S307: The same signal is transmitted from the base stations A and B to the mobile station X.

  After step S305, the channel gain information (CSI) between the base station A and the mobile station X and the CSI between the base station B and the mobile station X are collected in one place, and the precoding vector of each base station is calculated. You may be notified.

  As one form of mobile backhaul, configurations as shown in FIGS. 4A and 4B have been proposed. This configuration is a configuration in which a representative base station is installed in an optical line terminator (OLT) inside the station, and a base station is installed in an optical network unit (ONU) on the subscriber side (non-patent document). Reference 2). That is, base stations are connected by a PON system, and signal division multiplexing methods for PON systems between base stations include TDM (Time Division Multiplex), WDM (Wavelength Division Multiplex), and FDM (Frequency Division Multiplex). It can be illustrated.

  In this form, the representative base station responds to EPC on behalf of each base station connected to the ONU. Communication between the EPC and the base station is performed via the representative base station. In addition, communication between base stations can be realized using a PON section. The configurations of FIGS. 4A and 4B are more economical because the fibers can be concentrated compared to the case where communication is performed by connecting the related base stations with a dedicated fiber.

  FIG. 4A shows a configuration in which the representative base station 110 is added with the function of the OLT 140, the base station 120 is added with the function of the ONU 150, and the representative base station and the base station are connected by the PON system 130. For example, when a TDM-PON system such as GE-PON (IEEE802.3ah), 10G-EPON (IEEE802.3av), etc. is applied as the PON system, the function of the OLT is that the representative base station outputs in the downlink. A function of mapping data to be transmitted to an Ethernet (registered trademark) frame and transmitting it at a predetermined timing, and a function of extracting data from an Ethernet (registered trademark) frame received in the uplink. On the other hand, the ONU function refers to a function of extracting data from an Ethernet (registered trademark) frame received in the downlink, or a predetermined timing by mapping data output from a base station in the uplink to an Ethernet (registered trademark) frame. Includes the ability to send in.

  In FIG. 4B, adapters 210 and 230 are added between the representative base station 110 and the OLT 140 and between the base station 120 and the ONU 150, respectively, and the representative base station and the base station are connected by the PON system. The function of the adapter between the representative base station and the OLT includes a function of converting a downlink signal output from the representative base station into a signal in a format that can be recognized by the input interface of the OLT, and an upstream signal output from the OLT Includes a function to convert the signal into a format that the interface can recognize. On the other hand, the function of the adapter between the ONU and the base station is that the downstream signal output from the ONU is converted into a signal of a format that can be recognized by the input interface of the base station, or the upstream signal output from the base station is Includes the ability to convert the signal into a recognizable format.

"MIMO and inter-cell cooperative transmission / reception technology in LTE-Advanced", NTT DOCOMO Technical Journal Vol. No. 18 2 p. 22-30 Chathurika Ranaweera et al. , “Next Generation Optical-Wireless Converged Network Architectures”, IEEE Network, pp22-27.

  When performing JT, it is necessary to transmit user data of a mobile station to be subjected to JT from one base station to another base station.

  Here, in the configuration of FIGS. 4A and 4B, one fiber is shared by a plurality of ONUs. For this reason, as the number of base stations requesting JT increases and as the number of base stations participating in JT increases, the bandwidth of the PON section necessary for transferring user data increases, and another user There is a problem that a band for transmitting data is insufficient.

  An object of the present invention is to prevent an increase in the bandwidth of a PON section necessary for transferring user data even if the number of base stations requesting JT increases.

  The present invention makes it possible to suppress an increase in PON bandwidth that increases with JT by broadcasting data to all base stations using the multicast function of PON.

A communication method of a distributed radio communication base station system according to the present invention includes:
Representative base station,
A plurality of base stations that communicate wirelessly with mobile stations in the cell;
The representative base station side has an OLT (Optical Line Terminal) and the base station side has an ONU (Optical Network Unit), and PON (Passive) that multiplex-transmits signals between the representative base station and the base station Optical Network) system,
A communication method of a distributed radio communication base station system comprising:
At a predetermined time, data to the mobile station is distributed from the OLT to each ONU using multicast communication.

The distributed radio communication base station system according to the present invention is:
Representative base station,
A plurality of base stations that communicate wirelessly with mobile stations in the cell;
A PON system that has an OLT on each of the representative base stations and an ONU on each of the base stations, and multiplex-transmits signals between the representative base station and the base station;
A distributed wireless communication base station system comprising:
At a predetermined time, data to the mobile station is distributed from the OLT to each ONU using multicast communication.

  The present invention distributes data to the mobile station held by the representative base station at a predetermined time from the OLT to each ONU using multicast communication. Therefore, when communication between base stations occurs, Data can be transmitted to each base station. At this time, since multicast transmission enables transmission by one transmission, even if the number of base stations requesting JT increases, an increase in the bandwidth of the PON section necessary for transferring user data is prevented. Can do.

  In the present invention, the predetermined time is a case where the representative base station holds data for which a transfer request has occurred between base stations.

  In the present invention, the predetermined time is when the communication quality of the mobile station deteriorates due to signal interference between adjacent base stations or propagation loss between base stations and terminals.

  In the present invention, the data to the mobile station is the same downlink signal transmitted from an adjacent base station to the mobile station in order to perform coordinated transmission / reception between base stations.

  The above inventions can be combined as much as possible.

  According to the present invention, it is possible to prevent an increase in the bandwidth of the PON section necessary for transferring user data even if the number of base stations that request JT increases.

An example of the communication environment in a cellular system is shown. It is a schematic diagram which shows the 1st example of cooperation transmission / reception between base stations. It is a schematic diagram which shows the 2nd example of cooperation transmission / reception between base stations. An example of the sequence of the coordinated transmission / reception between base stations is shown. The 1st example of the structure which connects between a representative base station and base stations by a PON system is shown. The 2nd example of the structure which connects between a representative base station and base stations by a PON system is shown. An example of a coordinated transmission / reception sequence between base stations related to the present invention when X2 communication is applied to a distributed radio communication base station system in which a representative base station and a base station are connected by a PON is shown. An example of the JT procedure according to the first embodiment will be shown. An example of the JT procedure according to the second embodiment will be shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  In the distributed radio communication base station system according to the embodiment of the present invention, a plurality of base stations 103A and 103B that perform radio communication with a mobile station 101 in a cell are connected by one representative base station 110 and a PON system 130. . As a signal multiplexing method of the PON system, TDM (Time Division Multiplexing), WDM (Wavelength Division Multiplexing), FDM (Frequency Division Multiplexing) and the like can be selected.

  The configuration for connecting the representative base station 110 and the base stations 103A and 103B by the PON system is arbitrary. For example, the configuration shown in FIG. 4A is the configuration shown in FIG. Also good. Although the number of base stations connected by the PON can be an arbitrary number of 2 or more, in the present embodiment, a case where there are three base stations will be described for easy understanding.

(Embodiment 1)
In the first embodiment, when a certain base station needs to transfer user data to two or more other base stations, the representative base station transmits the user data to each base station by multicast from the representative base station side. Issue an order. A flowchart when the first embodiment is applied is shown in FIG. Hereinafter, an operation procedure in which the base station A cooperates with two base stations (base station B and base station C) will be described.

Step S601: Data addressed to the mobile station X is transmitted from the OLT to the base station A.
Step S602: The base station A acquires information on neighboring cells based on information from the mobile station X. Specifically, peripheral base station information (peripheral base station measurement result) such as the signal reception level of the downlink signal from the adjacent cell and the signal-to-noise interference power ratio (SINR) reported from the mobile station X is used.
Step S603: When the reception level of the signal from the adjacent cell reaches a preset threshold value, the base station A determines that the mobile station X exists at the end of the cell with the adjacent cell. At the same time, the base station B and base station C to be subjected to JT are specified. Base station A makes a JT request to base station B and base station C. At this time, control information such as radio band allocation information regarding the mobile station X is notified.
Step S604: The base stations B and C determine whether or not cooperation with the base station A is possible. The case where the base station B determines that the cooperation is impossible occurs, for example, when a resource shortage occurs, for example, the radio band of the mobile station X transmitted from the base station A is not free due to the radio band allocation of the base station B. sell.
Step S605: The base station B and the base station C return to the base station A whether or not cooperation is possible.
Step S606: The base station A requests the representative base station to transfer data addressed to the mobile station X to the base stations B and C. The data of the mobile station X may be transmitted from the base station A to the representative base station. Alternatively, the data transmitted from the representative base station to the base station A can be sent from the base station A to the mobile station X by leaving the data in the buffer until a certain time later. The data addressed to the mobile station X can be obtained.
Step S607: The representative base station multicasts the data of the mobile station X to the base station B and the base station C.
Step S608: The same signal is transmitted from the base stations A, B and C to the mobile station X.

  After step S605, the channel gain information between the base station A and the mobile station X, the channel gain information between the base station B and the mobile station X, and the channel gain information between the base station C and the mobile station X are collected in one place. Alternatively, the precoding vector of each base station may be calculated and notified.

  The signal from the base station A to the base station B and the base station C may be turned back anywhere in the representative base station, adapter, OLT, and optical signal branch circuit.

  Further, the first embodiment can be applied even when the number of base stations participating in JT is set to an arbitrary value as well as three.

  The embodiment 1 can also be applied when the base station A issues a cooperation request to the base station B and the base station C (step S603). That is, the base station A requests the representative base station to transmit a cooperation request to the base stations B and C, and the representative base station transmits the cooperation request to the base stations B and C by a multicast function. .

  As described above, according to the present invention, it is possible to transfer user data to base stations participating in JT with a single transmission.

FIG. 5 shows a case where the related JT procedure is applied to the configuration of FIG.
Step S501: Data addressed to the mobile station X is transmitted from the representative base station to the base station A.
Step S502: The base station A acquires information on neighboring cells based on information from the mobile station X.
Step S503: The base station A transmits a cooperation request to the representative base station, and the representative base station transmits a cooperation request from the base station A to the base stations B and C.
Step S504: The base station B performs resource confirmation.
Step S505: The base stations B and C respond to the representative base station as to whether or not cooperation is possible, and the representative base station notifies the base station A of the base station that is the cooperation possible response (cooperation response).
Step S506: The base station A transmits the data of the mobile station X to the representative base station, and the representative base station transmits the data of the mobile station X to the base stations B and C.
Step S507: The same signal is transmitted from the base stations A, B and C to the mobile station X.

  It can be seen that the JT procedure shown in FIG. 6 of the first embodiment uses fewer PON downlink bands for user data transfer than the JT procedure shown in FIG. For this reason, the present invention can prevent an increase in the bandwidth of the PON section necessary for transferring user data even if the number of base stations requesting JT increases.

(Embodiment 2)
In the second embodiment, the representative base station needs to transfer the user data addressed to which mobile station to which base station from these signals by using the fact that the JT cooperation request or cooperation response from the base station is returned by the representative base station. The user data is transmitted from the representative base station to each base station by multicast. FIG. 7 shows a flowchart when the second embodiment is applied. Hereinafter, an operation procedure in which the base station A cooperates with two base stations (base station B and base station C) will be described.

Step S701: Data addressed to the mobile station X is transmitted from the OLT to the base station A.
Step S702: Based on the information from the mobile station X, the base station A acquires information on neighboring cells. Specifically, information such as the signal reception level of the downlink signal from the adjacent cell and the signal-to-noise interference power ratio (SINR) reported from the mobile station X is used.
Step S703: When the reception level of the signal from the adjacent cell reaches a preset threshold value, the base station A determines that the mobile station X exists at the end of the cell with the adjacent cell. At the same time, the base station B and base station C to be subjected to JT are specified. The base station A makes a JT request (cooperation request) to the base station B and the base station C via the representative base station. At this time, control information such as radio band allocation information regarding the mobile station X is notified. At the same time, the representative base station receives this cooperation request and confirms to which mobile station user data needs to be transmitted.
Step S704: The base station B and the base station C confirm resources.
Steps S705 and S706: The base station B and the base station C return to the base station A whether or not cooperation is possible (S705). At the same time, the representative base station receives this cooperation permission / inhibition and confirms to which base station the data addressed to the mobile station X needs to be transmitted (S706).
Step S707: The representative base station multicasts the data of the mobile station X to the base station B and the base station C. The data of the mobile station X can be obtained by having the base station A once transmit to the representative base station. Alternatively, even after transmission from the representative base station to the base station A, data can be obtained by leaving the data in the buffer and outputting the data.
Step S708: The same signal is transmitted from the base stations A, B and C to the mobile station X.

  After step S705, the channel gain information between the base station A and the mobile station X, the channel gain information between the base station B and the mobile station X, and the channel gain information between the base station C and the mobile station X are collected in one place. Alternatively, the precoding vector of each base station may be calculated and notified.

  The signal from the base station A to the base station B and the base station C may be turned back anywhere in the representative base station, adapter, OLT, and optical signal branch circuit. In this case, the returning device has a function of confirming a cooperation request and a cooperation response from the base station and transmitting user data by a multicast function.

  Further, the embodiment 2 can be applied even when the number of base stations participating in the JT is set not only to 3 but also to an arbitrary value.

  In the JT procedure shown in FIG. 7 of the second embodiment, it can be seen that the number of times of using the PON downstream band for transferring user data is reduced compared to the JT procedure shown in FIG. For this reason, the present invention can prevent an increase in the bandwidth of the PON section necessary for transferring user data even if the number of base stations requesting JT increases.

  The present invention can be applied only by changing the representative base station without changing the base stations A, B, and C. However, at this time, since the base stations A, B, and C follow the conventional communication flow, data addressed to the mobile station X is transmitted from the base station A after step S705. As a method of preventing this data from using the bandwidth of the PON section, a method of discarding user data sent from the base station A by the adapter 230 or the ONU 150 attached to the base station A, A method of discarding data addressed to the mobile station X at the representative base station is conceivable.

  The present invention can be applied to the information communication industry.

101: Mobile stations 102A, 102B: Cells 103A, 103B: Base station 110: Representative base station 120: Base station 130: PON system 135: Optical signal branch circuit 140: OLT
150: ONU
210, 230: Adapter

Claims (6)

Representative base station,
A plurality of base stations that communicate wirelessly with mobile stations in the cell;
The representative base station side has an OLT (Optical Line Terminal) and the base station side has an ONU (Optical Network Unit), and PON (Passive) that multiplex-transmits signals between the representative base station and the base station Optical Network) system,
A communication method of a distributed radio communication base station system comprising:
A communication method of distributing data to the mobile station from the OLT to each ONU using multicast communication when the representative base station holds data for which a transfer request has occurred between base stations . Interference or base station signals between neighboring contact base station - when the communication quality of the mobile station causes the propagation loss between the terminals is lowered, the data transfer request is generated between base stations, the representative base station holds If it has, the communication method according to claim 1, characterized in that delivering the data to the mobile station from the OLT using the multicast communication to each ONU. The communication method according to claim 1 or 2 , wherein the data to the mobile station is the same downlink signal transmitted from an adjacent base station to the mobile station in order to perform coordinated transmission / reception between base stations. Representative base station,
A plurality of base stations that communicate wirelessly with mobile stations in the cell;
A PON system that has an OLT on each of the representative base stations and an ONU on each of the base stations, and multiplex-transmits signals between the representative base station and the base station;
A distributed wireless communication base station system comprising:
A distributed radio communication base station system that distributes data to a mobile station from an OLT to each ONU using multicast communication when a representative base station holds data for which a transfer request has occurred between base stations. Interference or base station signals between neighboring contact base station - when the communication quality of the mobile station causes the propagation loss between the terminals is lowered, the data transfer request is generated between base stations, the representative base station holds 5. The distributed radio communication base station system according to claim 4 , wherein data to the mobile station is distributed from the OLT to each ONU using multicast communication . 6. The distributed wireless communication according to claim 4, wherein the data to the mobile station is the same downlink signal transmitted from an adjacent base station to the mobile station in order to perform coordinated transmission / reception between base stations. Base station system.

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